1. Field of the Invention
The present invention relates to an image display apparatus using a display device such as an LCD (liquid crystal display) in which pixels are arranged in a mosaic pattern.
2. Description of the Related Art
In an image display apparatus, such as an LCD, using a display device in which a plurality of pixels are arranged in a mosaic pattern, in order to enhance a resolution, it is necessary to increase the number of pixels. It is impossible to unduly increase the number of the pixels or to unduly decrease a gap between the pixels due to the productive yield.
For this reason, in order to form a large-scale image field in such an image display apparatus, a mesh caused by pixel dots or gaps between the pixels (for example, at portions of LCD black stripes) is noticeable for the observer and difficult to watch. Also, in such a color image display apparatus, a color filter for three principle colors or three kinds of colors corresponding to the three principle colors is disposed on a front face of the above-described pixels at a predetermined repeated cycle. However, if the image field is enlarged, the pixel dot cycle at which the same color filter is disposed is noticeable and difficult to watch.
In CCD cameras, an electric treatment with a low pass filter makes it possible to cause the gap between the pixels to be unnoticeable. However, in an image display apparatus such as an LCD display apparatus, since it is necessary to fill the gap between the pixels after the formation of light, it is difficult to-make the pixel dots or mesh unnoticeable through the electric treatment. A method for fogging a lens focal point on the observer side has been proposed as a convenient method but a signal is also vague together. This is not preferable.
Therefore, some technology (for example, Japanese Patent Application Laid-Open No. Sho 59-214825, and Japanese Patent Application No. Hei 4-306003) has been proposed in which a diffuser (optical filter) having an optical filter face which is composed of a diffraction lattice or a micro prism group is provided on a front face of a display device such as an LCD, light from a single pixel is diffused into a plurality of rays of light, an image of the single pixel is formed on focus as an image (virtual image) of a plurality of pixels on a retina of the observer to thereby perform the diffusion of the pixel, and a focal position of the diffused image is located at the mesh position between the pixels to thereby make unnoticeable the mesh between the pixels.
FIGS. 13A to 13F show an example of a relationship among the pixel diffusion number, the resolution and the mesh reduction level. For the sake of simple explanation, the pixel diffusion in a lateral direction (X axis direction) of the display image will be explained with reference to this example but it should be noted that, in case of this example, the pixel diffusion is effected in a direction perpendicular to that direction, i.e., in a longitudinal direction in the same manner. Incidentally, in FIG. 13, the ordinate axis designates the luminance brightness, and the abscissa axis designates the spatial arrangement distance. Examples of FIGS. 13A to 13F are the cases where the diffused images of the respective pixels have the same luminance brightness.
FIG. 13A represents a pixel array along the X axis direction. In case of a black and white display device, ones shown by the solid lines are the neighboring pixels and a pixel cycle in the X axis direction is indicated by PCx. Also, in case of a color display device, for example, if the pixels shown by the solid lines are pixels in green, blue pixels and red pixels are present between the green pixels as indicated by dotted lines. Then, in this case, PCx is the same color pixel cycle and each cycle of the green, blue and red pixels is represented by PCx/3.
FIGS. 13B to 13F show the cases where the diffraction lattice or the micro prism is used and the respective pixels are uniformly diffused between the neighboring pixels under the condition that the diffused images of the respective pixels have the same luminance brightness.
FIG. 13B shows a case where a two-pixel diffusion for a shift by .+-.PCx/4 is effected to the original pixel position. The amount of shift (This is an interval between the pixels after the diffusion. This will be applied in the following description) is PCx/2.
FIG. 13C shows a case where a three-pixel diffusion for a shift by .+-.PCx/3 and zero is effected to the original pixel position. The shift amount is PCx/3.
FIG. 13D shows a case where a four-pixel diffusion for a shift by .+-.PCx/8 and .+-.3PCx/8 is effected to the original pixel position. The shift amount is PCx/4.
FIG. 13E shows a case where a six-pixel diffusion for a shift by .+-.PCx/12, .+-.3PCx/12 and .+-.5PCx/12 is effected to the original pixel position. The shift amount is PCx/6.
FIG. 13F shows a case where a nine-pixel diffusion for a shift by zero, .+-.PCx/9, .+-.2PCx/9 and .+-.3PCx/9 is effected to the original pixel position. The shift amount is PCx/9.
From the above-described cases, it is understood that, in the case where the respective pixels are diffused uniformly between the neighboring pixels, the relationship between the image diffusion number n and the shift amount S is given as follows: EQU S=PCx/n
Also, assuming that, in this case, M is the gap (hereinafter referred to as a pixel mask interval) through which light of the neighboring pixels (light of color corresponding to the pixel in case of the color) is not caused to pass, the following equation is given: EQU M=S-A
where A is the aperture width in the shift direction of the pixel.
In case of the six-pixel diffusion of the case shown in FIG. 13E, it will be understood that the outline between the pixels is almost filled, and M=0 is established so that the mesh is not noticeable. Also, in case of the nine-pixel diffusion of the cases shown in FIG. 13F, it will be understood that, as shown, a change of luminance brightness (non-uniformity in luminance brightness) appears due to the overlapped portion of the diffused image.
If a distance from a center of a single pixel to an edge of the diffused pixel in the subject pixel (i.e., edge of the display image of the subject pixel) is defined as an "edge spread" amount (E1 to E9), it will be understood that, as shown, the smaller the pixel diffusion number, the smaller the edge spread amount will become to thereby make it possible to indicate the clearer image. However, if the pixel diffusion number is small, in the case where a human eyes' low pass filter effect is not expected due to the large size of the display image, parts that are not luminous between the neighboring pixels are recognized as a mesh in a two-dimensional display, which degrades the image observation quality.
Subsequently, in FIG. 13G, the three-pixel diffusion is carried out by shifts of .+-.PCx/2 and zero by the optical filter surface 30a made of, for example, micro prisms. When the luminous level of the image having the shift amount of zero is represented by 1, the luminance brightness of the shift amount of .+-.PCx/2 is represented by 1/2. The diffusion image of the shift amount .+-.PCx/2 has the luminance brightness of 1 by the overlapping of the neighboring pixels. In this example, in spite of the small pixel diffusion number in comparison with the luminance brightness olf 1:1, the spread amount is large.
From the review of FIGS. 13A to 13G, it is understood that the conditions of the optimum pixel diffusion are preferably:
to effect the diffusion to the position that bisects the same color pixel pitch; and PA1 to increase the number of the diffusion more. PA1 to make the diffusion luminous ratio equal. PA1 In the example shown in FIGS. 13A to 13G as described above, if the PA1 a display device 1 having an image pattern in a mosaic patter; and PA1 an optical filter surface 3A disposed on a front face of said display device for diffusing each pixel of said display device into a plurality of parts by utilizing diffraction or refraction, PA1 characterized in that said optical filter surface 3A performs the pixel diffusion so that a sight angle, of a gap which does not pass light between the neighboring pixel after the pixel diffusion, as viewed from the observer on the focal plane on which the image displayed by said display device is observed by an observer is substantially a predetermined recognizable limit view angle of the observer.
In order to suppress the edge spread, it is, preferable to decrease the number of diffusion and
image magnification is large and the small amount of mesh would make the observation difficult, it is most preferable to use the six-pixel diffusion shown in FIG. 13E.
Incidentally, under the above-described condition, the optimum value for the pixel diffusion number changes in accordance with the image magnification. Namely, in case of the small magnification, since the mesh is not noticeable, in some cases, it is generally preferable not to increase the diffusion number to the maximum level and the edge spread is small.
As described above, the mesh due to the gap between the pixels in the display device in which the pixels are arranged in a mosaic pattern may be made noticeable and at the same time the same color pixel dot cycle may be made noticeable.
By the way, in the case where the observer watches the image on the display device, it is general that the observation is made to adjust the lens so that the display image is focused on the imaging face.
However, in the case where the pixel diffusion is effected so as to completely make the mesh noticeable and its image is displayed on the imaging face, it has been found that it is difficult to perform the focusing. Namely, it is difficult for the observer to positively recognize the focused condition from the observed image.
In view of the above-described defects, an object of this invention is to provide an image display apparatus in which the focusing may readily be made while displaying the image in which the mesh is noticeable.